The present invention relates to an ultrasonic welding device which, when connecting together plastic moldings by ultrasonic welding, can provide the optimum connecting condition as well as a method for controlling welding in such ultrasonic welding.
Also, the present invention relates to a method and a device for welding together two reels into an integrally connected reel for use in a magnetic tape cartridge. In particular, the present invention relates to a method and a device for welding together upper and lower reels into a reel for use in a magnetic tape cartridge, in which the upper reel includes a reel hub with engagement means for rotation driving disposed on the bottom outer surface thereof, and a flange portion projecting in the radial direction of the upper reel from the lower end outer periphery of the reel hub; and, the lower reel includes a circular opening through which the bottom outer surface of the reel hub having the engagement means can be inserted, and a projecting rib to be welded. That is, the present invention relates to a welding device for welding the lower reel to the periphery of the engagement means of the reel hub of the upper reel.
Conventionally, as a magnetic tape cartridge used as a recording medium in a computer and the like, there is known a structure of a type that a magnetic tape is wound on a single reel. This magnetic tape cartridge is used as the external memory of a computer, while important information is stored in the magnetic tape cartridge. For this reason, the magnetic tape cartridge is structured such that not only it is free from troubles such as tape jamming and the like but also the magnetic tape thereof is prevented from being drawn out unpreparedly.
In FIG. 1, there is shown a conventional magnetic tape cartridge 1 which is used as the magnetic recording medium of a computer such as a tape streamer or the like. As shown in FIG. 1, the conventional magnetic tape cartridge 1 is structured such that a magnetic tape 20 is wound on a single reel 3 composed of an upper reel 4 and a lower reel 5 connected together by ultrasonic welding, while the reel 3 is rotatably stored within a cartridge case which is composed of an upper cartridge 2a and a lower cartridge 2b fastened together by screws 19.
The upper reel 4 is formed of polycarbonate resin with glass fibers contained therein and includes an upper flange 4a in the central portion of which there is formed a recessed portion 4b. Along the outer periphery of the upper flange 4a, there is formed a gear portion 4c.
Also, a ring-shaped bearing 6 is pressure inserted into and fixed to a cylindrical-shaped rib formed in the recessed portion 4b, while a spring plug 7 is pressure inserted into and fixed to a hole formed in the central portion of the bearing 6. And, a reel spring 8 is mounted on the spring plug 7, while the reel spring 8 presses against the reel 3 downwardly and holds the reel 3 in a freely rotatable manner.
On the other hand, the lower reel 5 is formed of polycarbonate resin and includes a lower flange 5a; and, in the periphery of a hole formed in the central portion of the lower flange 5a, there is provided a projecting portion 5b for ultrasonic welding, while the projecting portion 5b is to be ultrasonically welded to the shoulder of the recessed portion 4b of the upper reel 4.
The reel 3, when the cartridge is not in use, is secured by reel brakes 50 and 51, which are respectively energized properly by their associated torsion springs 12 for braking, so that the reel 3 is prevented against an unexpected rotation. Also, when the magnetic tape cartridge 1 is not in use, with the magnetic tape 20 wound completely on the reel 3, leader tape 21 (means which is used by a computer device for introducing the magnetic tape 20 into a tape passage) mounted on the end of the magnetic tape 20 is secured to the leading end portion of a hook 18 which is incorporated into the cartridge near the side face of the cartridge.
And, on the opening portion of the cartridge for pulling out the magnetic tape 20, there is mounted a lid 30 which is properly energized by a torsion spring 15 for lid energization and can be opened and closed in the cartridge plane direction. When the cartridge is not in use, the lid 30 is secured by a lock member 40 which is properly energized by a compression spring 16 so that the lid 30 is prevented against rotation. Also, on the opposite side of the lid 30, there is incorporated a write protect 17.
The leader tape 21, which can be engaged with engagement means for introducing the magnetic tape 20 to the tape passage of a recording and reproducing device, is connected to the magnetic tape 20, for example, by splicing.
In a method for connecting by ultrasonic welding the upper reel 4 and lower reel 5 of the magnetic tape cartridge 1 structured in the above-mentioned manner, as has been described before, the projecting portion 5b, which is provided along the peripheral edge of the opening or hole formed in the central portion of the lower flange 5a of the lower reel 5, is engaged with the shoulder of the peripheral edge of the downwardly projecting end of the recessed portion 4b of the upper reel 4; and, in this engaged state, by applying a given pressure between the projecting portion 5b and recessed portion 4b shoulder to thereby excite them ultrasonically, so that, while melting the projecting portion 5b, the two reels 4 and 5 are connected together.
Also, FIG. 2 shows a welding device for working or welding the above-mentioned reel 3 ultrasonically. An ultrasonic welding device 60 shown in FIG. 2 comprises a working bed 61, a vertical frame 62 erected on one side of the bed 61, an air cylinder 63 suspended from the head portion of the vertical frame 62, a lifting frame 67 which is connected through a pressurization sensor 65 to a plunger 64 projecting into the lower portion of the air cylinder 63 and can be moved along a linear guide 66 disposed inside the vertical frame 62 in such a manner that it can be raised and lowered, an ultrasonic welder unit 68 supported vertically by the lifting frame 67, and a displacement sensor 69 for detecting the motion or displacement of the ultrasonic welder unit 68.
The ultrasonic welder unit 68 is composed of three mutually continuing parts, that is, a converter 70, a booster 71 and a hone 72 to be contacted with a workpiece or a member to be worked, which are arranged sequentially in a descending order from the top of the ultrasonic welder unit 68.
On the other hand, on the upper surface of the bed 61, there is disposed a receive base 74 through a fine adjusting base 73. While one workpiece, that is, the upper reel 4 is fitted with and placed on the receive base 74 and the other workpiece, that is, the lower reel 5 is fitted with the upper surface of the upper reel 4, by lowering the ultrasonic welder unit 68, the two upper and lower reels 4 and 5 are pressurized and excited to thereby produce friction heat between them, so that the mutually connecting surfaces of the upper and lower reels 4 and 5 can be welded together.
The thus structured air cylinder 63 and ultrasonic welder unit 68 are driven and controlled by a control unit 75 which outputs such instructions to the air cylinder 63 and ultrasonic welder unit 68 as correspond to the information that is input therein from the pressurization sensor 65 and displacement sensor 69.
The control unit 75, which is composed of a programmable controller or the like, not only can monitor variations in the respective parts during the reel working or welding operation in accordance with clock frequencies that are counted by a built-in timer, but also includes a display, a key board and the like (which are not shown) so that it is able to set various kinds of working or welding operations by inputting various numerical values.
In particular, the control unit 75 controls the air cylinder 63 in the following manner: that is, when a start switch 76 is turned on, while monitoring the detected condition from the load cell or pressurization sensor 65, the control unit 75 not only adjusts an air pressure supplied from an air cylinder driving air pressure source 77 to a given pressure through a pressure adjusting device 78 but also controls the air by opening or closing an electromagnetic valve 79; that is, when the electromagnetic valve 79 is opened, then the plunger 64 is projected to thereby lower the ultrasonic welder unit 68 down to a working or welding position, or when the electromagnetic valve 79 is closed, then the plunger 64 is retreated to its original position to thereby separate the ultrasonic welder unit 68 from the working or welding position.
Also, the control unit 75 controls the ultrasonic welder unit 68 in the following manner: that is, when the start switch 76 is turned on, while monitoring the detected condition of the linear encoder or displacement sensor 69, the control unit 75 starts an oscillator power source 80 and, at the same time, excites the ultrasonic welder unit 68 with the amplitude that is adjusted and set through an amplitude adjusting device 81.
In the above-mentioned conventional ultrasonic welding method, optimum pressure, amplitude and welding time are set according to the material and thickness of the workpiece, and the workpiece is worked uniformly under such set conditions. However, after the workpiece starts to melt, if the pressure and amplitude thereof are held constant until the working or welding is finished, then it is found that the workpiece is caused to deform.
In fact, for example, in the reel 3, the parallelism deviation between the upper reel 4 and lower reel 5 is worsened, which makes it easy to cause a so called surface slippage between the upper and lower reels 4 and 5, resulting in a high rate of occurrence of defective products.
On the other hand, when the workpiece is worked or welded under the conditions that are lower than the above-mentioned optimum set values, there occurs poor welding which not only causes the yield rate of the material to lower but also, even if the workpieces are the same in the material and thickness, causes the products to vary easily in quality.
And, when the workpieces -are welded together with the low pressure and low amplitude, it takes a longer time to weld them, which in turn lowers the productivity thereof.
Also, in the above-structured ultrasonic welding device 60, as shown in FIG. 3, there is produced a slight gap d between the fitting portion peripheral edge of the receive base 74 to be fitted with the upper reel 4 and the opening of the upper reel 4. That is, this gap causes the receive base 74 and upper reel 4 to play and, in the working or welding operation, there is produced such a vertical slippage as shown by arrows in FIG. 3, which in turn causes the yield rate of the material to lower.
To prevent such play, the gap margin may be set sufficiently small from the beginning. However, in this case, it is troublesome to install the upper reel 4 on the receive base 74 side and, especially, when the upper reel 4 is inserted automatically, such small gap margin provides the cause of wrong insertion. Therefore, it is indispensable to secure a certain degree of gap. That is, they are opposed to each other.
Further, in the above-structured ultrasonic welding device 60, as shown in FIG. 4, since the receive base 74 is structured such that the boss support portion 74b thereof is provided on and projected from the central position of the flange support portion 74a formed integrally therewith, when the upper reel 4 is placed on the upper portion of the boss support portion 74b and the flange portion 4a of the upper reel 4 is seated on the flange portion 74a of the receive base 74, they can be set in such a manner that there is produced a gap d between the top portion of the boss support portion 74b and the inner surface of the boss portion 4b due to the dimensional tolerance thereof or the like.
On the contrary, although not shown, while the inner surface of the boss portion 4b is set on the top portion of the boss support portion 74b in a close contact manner, the flange portion 4a can be set in such a manner that it is not seated on the flange support portion 74a but is separated therefrom.
Therefore, in the former case, after the lower reel 5 is mounted onto the upper reel 4 to thereby complete their setting, if the ultrasonic welder unit is lowered, then the upper and/or lower reels can be pushed by an amount corresponding to the gap d due to the collision inertia thereof, pressing forces applied in the working or welding operation, and the like, so that they can be deformed, which in turn causes the yield rate of the material to lower.
Also, in the latter case, due to the gap between the side surface of the boss support portion 74b and the inner wall surface of the boss portion 4b, the reel 4 can be vibrated while it is worked or welded, which, similarly to the above case, causes the yield rate of the material to lower.
The above-mentioned magnetic tape cartridge is structured such that, as shown in FIG. 1, the magnetic tape 20 is wound on the single reel 3 composed of the upper reel 4 and lower reel 5 connected together by ultrasonic welding, while the reel 3 is rotatably stored within the cartridge case 2 which is composed of the upper cartridge 2a and lower cartridge 2b fastened together by the screws 19 or the like.
The upper reel 4 of the above-mentioned single reel 3, as shown in FIGS. 5 and 6 as well, is composed of a reel hub 42 and a flange portion 43 which are united together into an integral body by means of synthetic resin: in particular, the reel hub 42 is formed in a bottomed cylindrical shape, and includes in the bottom portion outer surface thereof a plurality of securing teeth 42a serving as engagement means for rotation driving, and also includes a cylindrical portion 42b on the outer periphery of which the magnetic tape 20 can be wound; and, the flange portion 43 projects in the radial direction of the reel 4 from the outer periphery of the upper end of the reel hub 42, and includes in the outer peripheral edge thereof a plurality of restricting gears 43a with which the reel locks 50, 51 can be engaged when restricting the rotation of the reel 4 while the magnetic tape cartridge is not in use. As shown in FIG. 2, the bottomed recessed portion formed in the reel hub 42 is opened upwardly (in FIGS. 5 and 6, downwardly).
The lower reel 5 is formed in a disk shape which includes in the central portion thereof a circular opening 5d for insertion of the above-mentioned securing teeth 42a therethrough and, on the periphery of the opening 5d, there is projectingly provided a welding rib 5c which can be butted against a welding contact portion (stepped surface) 42c annularly formed in the periphery of the securing teeth 42a. And, as shown in FIG. 6, while the welding rib 5c is assembled on the bottom portion of the reel hub 42 of the upper reel 4, the lower reel 5 can be welded ultrasonically to the upper reel 4 by an ultrasonic welding device (which will be discussed later).
When the above-mentioned magnetic tape cartridge 1 is set in its corresponding external memory device or the like, then rotation driving means provided on the external memory device side is engaged with the securing teeth 42a of the reel 3 projecting into an opening 2c formed in the central portion of the lower cartridge 2b, and, at the same time, the lid 30 is opened by a tape pull-out mechanism provided on the external memory device side and thus the leader tape 21 is pulled into a given position in a tape running path, thereby allowing the data to be written into or read out from the magnetic tape 20.
The above-mentioned reel 3 for a magnetic tape cartridge must have a high dimensional accuracy in order for the magnetic tape 20 to be able to run stably with high accuracy and, for this reason, the operation to connect the upper reel 4 and lower reel 5 to each other by welding must be carried out carefully.
Now, FIG. 7 shows a conventional welding device 160 which is used to weld together the above-mentioned upper reel 4 and lower reel 5.
The conventional welding device 160 comprises a welding receive base 161 for supporting the upper reel 4 in the reversed state in which the flange portion 43 is disposed in the lower portion thereof, so that the welding receive base 161 can support the upper reel 4 from the bottom portion inner surface side of the reel hub 42, and a welding horn 162 which, with the lower reel 5 assembled to the bottom portion of the reel hub 42 of the upper reel 4, presses the annular rib 5b of the lower reel 5 against the upper reel 4.
And, as shown in FIG. 8, if, while the lower reel is pressed and energized properly by the welding horn 81, ultrasonic vibrations are given to the welding horn 81, then there are generated ultrasonic vibrations Y in the reel thickness direction. Due to the thus generated ultrasonic vibrations Y, as shown in FIG. 9, the welding rib 5c is melted and the thus melted resin of the welding rib 5c is then hardened, with the result that the upper and lower reels 4 and 5 can be welded together.
Also, as the welding receive base 161, there is used either a receive base 164 structured such that it supports the upper reel 4 by means of a flange contact portion 163 thereof which can be contacted with the surface of the flange portion 43 of the upper reel 4, or a receive base 165 structured such that it supports the upper reel 4 by means of the upper end face 166 of a center projecting portion which can be fitted with the bottomed recessed portion of the reel hub 42, while the flange contact portion 163 and upper end face 166 are both formed in a flat surface.
And, the flange contact portion 162a of the welding horn 162, which can be contacted with the annular rib 5b in order to apply the ultrasonic vibration energy to the welding rib 5c, is also formed in a flat surface.
However, in the above-mentioned conventional welding device 160, due to the ultrasonic vibrations applied from the welding horn 162, the upper reel 4 can be made to slip off in position in the radial direction thereof with respect to the welding receive base 161 or can be made to rotate with respect to the lower reel 5; that is, the upper reel 4 is not stabilized. This causes the upper and lower reels 4 and 5 to be welded unevenly, which in turn results in the lowered welding accuracy, the slippage of the surface of the lower reel, and other similar problems.
In view of this, in order to prevent the positional slippage and relative rotation of the upper reel 4 when the ultrasonic vibrations are applied thereto, the present inventors have studied the employment of a structure in which the welding receive base 161 is so arranged as to be fittable with the bottomed recessed portion of the reel hub 42 like the receive base 165 shown in FIG. 7, and the dimensional tolerance is reduced (for, example, down to 0.07 mm or less, preferably, down to 0.05 mm or less) so that the receive base 165 and reel hub 42 can be closely fitted with each other. However, when the dimensional tolerance is reduced in this manner, it takes time and labor to mount the reel hub 42 onto the receive base 165 and remove the former from the latter, which makes it impossible to enhance the productivity.
In particular, in connecting the upper reel 4 and lower reel 5 to each other by ultrasonic welding, the center projecting portion of the receive base 165 is fitted and inserted into the bottomed recessed portion of the reel hub 42. If the dimensional tolerance is small, then not only the positioning accuracy of the upper reel 4 with respect to the receive base 165 must be enhanced but also it is difficult to exhaust the air within the bottomed recessed portion of the reel hub 42. That is, if the center projecting portion of the receive base 165 is quickly inserted into the bottomed recessed portion of the reel hub 42, then there is generated an insertion resistance between them. And, also when the integrally welded reel 3 for a magnetic tape cartridge is removed from the receive base 165, there is generated a removing resistance between them, which makes it impossible to take out the reel 3 quickly.
Also, when the upper and lower reels 4 and 5 are welded together in this manner, the ultrasonic vibrations Y applied in the welding operation cause the respective contact portions of the upper and lower reels 4 and 5 (in particular, the respective contact portions of the welding rib 5c and welding contact portion 42c) to rub against each other, resulting in the shaved resin. And, if shaved powder 85 produced due to such shaved resin is left between the upper and lower reels 4 and 5, then there is a possibility that the shaved powder 85 can attach to the magnetic tape wound on the reel 3, thereby raising a possibility that some signals can be missed in the recording and reproducing operation of the magnetic tape cartridge.
Further, if the welding rib 5c melts excessively and is thereby welded excessively so that the melted welding rib 5c overflows into the tape winding area (that is, the outer peripheral area of the reel hub 42), as shown in FIG. 9, the lump 91 of melted and hardened resin 90 causes damage to the magnetic tape that is to be wound on the outer periphery of the reel hub.